They look like leftover gravel from a freshly laid asphalt road, but the black stones that spattered across the snow in the wake of the January 16th Michigan fireball were anything but terrestrial. They belonged to a tiny asteroid on a recent foray to the outer asteroid belt but now grounded for good on Earth.
Meteorite hunters swarmed to the strewn field near the Township of Hamburg in southeastern Michigan with heads down, walking frozen lakes, parks, and streets in the fall’s strewn field hoping to find a piece of interplanetary treasure. A few have had success, others have returned home with sore legs but grateful to join in the hunt.
Using a little ingenuity and basic geometry, Todd Slisher, executive director of the Sloan Museum and Longway Planetarium in Flint, Michigan, became one of the lucky ones. Slisher’s home security camera captured the shadow of the peak of his roof moving across the deck below like a shadow cast by a sundial gnomon. It also recorded the sound blast from the bolide’s breakup in the atmosphere, when the meteoroid shattered and began dropping what would soon become meteorites.
By measuring the angles of the roof shadow and the 104-second delay between the appearance of the fireball and its explosive crack-up, Slisher arrived at the distance (21 miles) and direction of the strewnfield from his home.
“It was just simple geometry,” he said.
He confirmed his back-of-the-napkin results with NASA Doppler weather data, which picked up the characteristic signature of falling meteoroid fragments. With a reasonably good idea of where to hunt, Slisher next organized a search team, contacting members of the Farmington Community Stargazers.
Two days after the fall, the party of five fanned out in a line 10 feet apart and walked a lake looking for out-of-place black stones. There were a few false alarms, including “frozen feces” sightings, but before long Slisher happened on a dark stone poking up from the thin snow cover.
“Oh my god, I think this is it,” he said.
Based on color, shape and classic indentations called regmaglypts in the stone’s surface, it appeared to be the real McCoy.
“I tapped it out of the snow with my gloves,” said Slisher. “We oohed and aahed over it then high-fived and fist-bumped before I wrapped it up in foil and put it in a plastic bag.”
It was the first meteorite Slisher ever found. Electrified by the find, the team continued their sweeps and found two more pieces that day, the largest measuring about 3.2 cm across. To preserve the newly arrived visitors from the damaging salt and oils of human touch, each was carefully wrapped in foil and bagged.
Interestingly, the five specimens were found in a line three-quarters of a mile long tracing the axis of the strewn field. The third and final find of the day was the clincher:
“The fusion crust was stuck to the ice which showed the rock’s gray interior,” said Slisher. “We knew then we had meteorites!”
Stony meteorites are primarily composed of silicate materials, which when fresh, look almost identical in color to concrete. This is particularly true with highly metamorphosed chondrites which this fall is believed to be.
One additional, solitary flake of fusion crust was also gathered. Judging from the curvature Slisher suspects that the mother rock may be a nice-sized piece just waiting to be found . . . reason to return to the site for another look.
According to NASA, this fireball was notable for its steep angle of entry, 21° from vertical. It also moved slowly because it approached Earth from the backside and then broke apart at an altitude of 15 miles, landing in the fields and lakes between the Township of Hamburg and Lakeland. Preliminary orbital elements suggest that the parent meteoroid followed an eccentric orbit that looped nearly out to Jupiter.
One of the meteorites is currently on display at the Longway Planetarium in Flint, another sits in a dark freezer. Keen on preserving any volatiles and organics the meteorite may contain, Slisher plans to send it to NASA. Proof that even extraterrestrial visitors aren't immune to red tape, he won't be able to do so until after the government shutdown ends.